Turn table speed variation question

Frogman et al. You've made some great points. In the last instance, the most famous case of pitch instability caused by the master tape is Kind of Blue. For decades I listened to the wobbly and flat piano tones on KOB, and it was actually part of the mystique of the LP. I once listened to one side (Blue and Green) over and over again from late evening until dawn. The music exactly fit my mood. (Well, I was in college, and there was a girl who dumped me.) Then they finally told us that the tape speed was off!!! Flat because of that; wobbly because of belt-drive pitch instability. I really can't get used to the "corrected" versions played on my "issue"-less direct- and idler-drive turntables. (Joking with Frogman.)

Speaking generally, authentic/original instrument recordings are acid tests for TT pitch stability.

Many orchestral instruments were redesigned in the 19th C. to produce a more forceful, projective tone. This was done to make them audible in the larger concert halls being built to accommodate an expanding middle class audience. To my ears, these more modern instruments place more energy behind the fundamental, at the relative expense of harmonics. (Lew and I discussed this before in another context.)

The older version of such instruments had a stronger harmonic envelope relative to the fundamental. This harmonic envelope is easily distorted into an inharmonious squawk by TT speed instabilities, even if the instabilities occur over very short time frames. Speed variations that occur between strobe measurements can be audibly destructive, yet not detectable by commonly used TT speed measuring instruments.

Play a selection of Hogwood, Harnoncourt and the like. If the TT speed isn't rock solid over all time spans, you'll hear it.

Dougdeacon, you are correct in your description of the harmonic
characteristics of period vs modern instruments. The opposite is believed
to be true by some (including some musicians) because modern
instruments' apparent brilliance is sometimes assumed to be the result of
increased harmonics (relative to the fundamental), when what is often the
case is the absence (or decrease) of specific harmonics due to
manipulation in design giving the sound a less complete harmonic
structure. This less complete harmonic structure can highlight upper
partials and give the modern instrument an edgy or "brilliant"
sound. The denser, sweeter sound of many period instruments is the result
of a more complete harmonic content.

I am not so sure about your contention that this more complete harmonic
structure would make the sound of period instruments more susceptible to
a tt's speed inaccuracies as all frequencies would suffer to the same
degree. However, you are quite correct about original instrument
recordings being an "acid test" for speed stability. But, IMO, the
main reason for this is what I pointed out in my previous post; the presence
or absence of vibrato. Music performed on period instruments normally is
played with very little or no vibrato. When this music was composed,
performance practice dictated very very sparse use of vibrato; only as an
occasional color as opposed to the constant use of vibrato that is common
today. The reason for this is that, for instance, a modern violin played with
no vibrato will sound louder than an original one, but dry and lifeless
because of (as you pointed
out) the diminished overtone content.

Thanks everyone for the input - I now have a very good understanding of possible causes - never thought about the off-centre hole - good one :-)

I had always thought it was due to the tape ,machine used in the recording process.

I can see how the pure pitch of a long note and the associated harmonics would contribute to the immediate identification of speed variations - to these ears anyway.

Thanks again for the input - very enlightening.

"Lew's right.
Any stringed instrument is particularly sensitive to minute speed deviations.
When I listen to acoustic guitar on my Victor TT-101 DD turntable with unequalled speed accuracy......an off-centre record hole will be mercilessly exposed. :-(" - Halcro

Not to digress too far, but since the thread is about speed accuracy, I do believe the word "unequaled" may be a contentious one. I doubt if the Victor is unequaled, however. What measure of accuracy is it?